1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for maintaining voice quality in a wireless network, and specifically to measuring the power and bit error rate on the up-link and down-link channels simultaneously.
2. Background and Objects of the Present Invention
Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications ever. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. Cellular networks have evolved into two different networks. The European cellular network uses the Global System for Mobile Communication (GSM) digital mobile cellular radio system. In the United States, cellular networks have traditionally been primarily analog, but recent advances have been incorporating digital systems within the analog networks. One such North American cellular network is the D-AMPS network, which is described hereinbelow.
With reference now to FIG. 1 of the drawings, there is illustrated a D-AMPS Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Switching Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16 therein. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which a Mobile Station (MS) 20 may move freely without having to send update location information to the MSC/VLR area 12 that controls the LA 18.
Mobile Station (MS) 20 is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other, and users outside the subscribed network, both wireline and wireless. The MS 20 may also include a Subscriber Identity Module (SIM) card 13, or other memory, which provides storage of subscriber related information, such as a subscriber authentication key, temporary network data, and service related data (e.g. language preference).
Each Location Area 12 is divided into a number of cells 22. The MSC 14 is in communication with a Base Station (BS) 24, which is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the geographical part of the cell 22 for which it is responsible.
With further reference to FIG. 1, the PLMN Service Area or cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information. The HLR 26 may be co-located with a given MSC 14, integrated with the MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIG. 1.
The VLR 16 is a database containing information about all of the Mobile Stations 20 currently located within the MSC/VLR area 12. If an MS 20 roams into a new MSC/VLR area 12, the VLR 16 connected to that MSC 14 will request data about that MS 20 from the home HLR database 26 (simultaneously informing the HLR 26 about the current location of the MS 20). Accordingly, if the user of the MS 20 then wants to make a call, the local VLR 16 will have the requisite identification information without having to reinterrogate the HLR 26. In the aforedescribed manner, the VLR and HLR databases 16 and 26, respectively, contain various subscriber information associated with a given MS 20.
Currently, speech and data are transmitted from the BS 24 to the MS 20 on a down-link channel 30 and from the MS 20 to the BS 24 on an up-link channel 32. If the power transmitted by the BS 24 on the down-link 30 is too high, in some areas of the cell 22, e.g., near the corners of the cell 22, the customer will see a good signal on the MS 20 power meter, but the MS 20 will not be able to access the system, because the up-link 32 power of the MS 20 is not strong enough. In addition, even if the MS 20 can access the system, the speech quality on the up-link 32 is usually poor. Furthermore, in order to reduce co-channel interference, which is the interference caused by the use of the same frequency within two different clusters of cells 22, the power on the down-link 30 must be minimized.
The BS 24 has two receiver antennas, for diversity, and one transmitting antenna. In certain areas of the cell 22, the reception on the down-link 30 can be poor, e.g., the bit error rate (BER) is high, because the transmitting antenna is not suitably located for this area of the cell 22, but, at the same time, the reception on the up-link 32 can be good, e.g., the BER is low, because at least one of the receiving antennas is located satisfactorily with respect to the same area of the cell 22. Therefore, in order to maintain a system with balance links, e.g., up-link 32 and down-link 30, both in power and in the BER, the power and BER must be known at each point in the cell 22 for both the up-link 32 and the down-link 30, simultaneously.
In order to sufficiently analyze the power and BER for the up-link 32 and down-link 30, a technician must drive the area covered by the cell 22 and compare both in real time and in off-line, the difference between the up-link 32 and the down-link 30 for both the signal strength and the BER. Currently, there are three options for performing these measurements. First, the technician can drive the area and measure only the down-link 30. However, in this case, the down-link 30 and the up-link 32 can not be compared at every point in the cell 22. Secondly, the technician can compare the logs from the MSC 14, which show the reading for both the up-link 32 and the down-link 30 at the same time. However, in this case, the exact location of the MS 20 within the cell 22 is not available. Finally, as discussed in Suutarinen, WO 97-342024, both the up-link 32 and down-link 30 can be measured simultaneously with knowledge of the location, but the setup has to be done in the MSC 14 and two technicians are required: one in the MSC 14 measuring and receiving the power and BER, and one driving the cell 22 with an MS 20. Thus, the above solutions do not give a real time solution in the field for the drive technician.
It is, therefore, an object of the invention to perform real time measurements in the field of both power and BER for both the up-link and down-link substantially simultaneously.
It is a further object of the invention to allow the power and BER measurements to be performed in the field by one technician.
It is still a further object of the invention to have all of the information, e.g., up-link and down-link power and BER measurements, as well as the geographical location of the mobile terminal, within the mobile terminal itself in order to analyze the system and make decisions more easily, faster and more efficiently.